C# – Regular Expression to detect repetition within a string


Is it possible to detect repeated number patterns with a regular expression?

So for example, if I had the following string "034503450345", would it be possible to match the repeated sequence 0345? I have a feeling this is beyond the scope of regex, but I thought I would ask here anyway to see if I have missed something.

Best Solution

This expression will match one or more repeating groups:


Here is the same expression broken down, (using commenting so it can still be used directly as a regex).

(?x)  # enable regex comment mode
(     # start capturing group
.+    # one or more of any character (excludes newlines by default)
)     # end capturing group
(?=   # begin lookahead
\1+   # match one or more of the first capturing group
)     # end lookahead

To match a specific pattern, change the .+ to that pattern, e.g. \d+ for one or more numbers, or \d{4,} to match 4 or more numbers.

To match a specific number of the pattern, change \1+, e.g to \1{4} for four repetitions.

To allow the repetition to not be next to each other, you can add .*? inside the lookahead.